Abstract

Activation of -type III-V semiconductors with cesium and oxygen has been widely used to prepare negative electron affinity (NEA) photocathodes. However, the nature of the chemical species on the surface after the activation is not well understood. In this study, InP NEA photocathodes activated with cesium and oxygen are studied using synchrotron radiation photoelectron spectroscopy, also called photoemission. Based on the O core level as well as the valence bandspectra, Cs peroxide and Cs superoxide are identified on the InPsurface. Transformation from Cs peroxide to Cs superoxide is observed after the activation, and is probably the major reason for the decay of the quantum yield of the photocathode. The oxidation of the InP substrate is also observed with elapse of time, adding to the decay of the quantum yield.

Received 05 April 2007Accepted 18 August 2007Published online 05 October 2007

Acknowledgments:

This work was performed under Army Contract Nos. DAA07-00-3-L-517 and DAAD19-02-1-0396. This work is also supported by the Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences. We would also like to thank the SSRL staff for their support.